The immature bird or mammal depends on external sources of heat to maintain homeothermy and, in turn, is sensitive to alterations in thermal input. Exposure to microwaves results in the deposition of energy into the animal; the magnitude of the thermalization is related to both microwave intensity and ambient temperature. Unfortunately, it is difficult to expose the mammal to microwaves during perinatal development without maternal influence. Birds are free of such maternal influence. The proposed study will 1) construct an avian model of thermoregulatory development which permits analysis of response to environmental stress, free of any maternal interaction, and 2) use this model to determine stress-response relationships between microwave exposure and ambient temperature. Fertile quail eggs will receive repeated (8 h/day) microwave (5 or 20 mW/cm2) or sham exposures to 2450 MHz continuous microwaves. In Experiment I, egg temperature will be maintained at normal level during exposure to determine effects of microwaves per se. In Experiment II, ambient temperature will be controlled at levels below incubation temperature during microwave exposure to examine interactions between microwave intensity and ambient temperature. Before the eggs hatch, physiological tests will be conducted to determine both metabolic and body temperature responses that may result from previous treatments. Untreated hatchlings (2-15 days after hatching) will be subjected to both acute (Experiment III) and repeated (Experiment IV) microwave (5 or 20 mW/cm2) or sham exposures at different ambient temperatures (20-30 degrees C). Acute exposures will last up to 24 h and the animals will be tested immediately afterwards to determine short-term changes in thermoregulatory ability. Repeated exposures will be for 10 continuous days at 8 h/day and the animals tested following the entire exposure period to determine adaptive changes in thermoregulatory ability. In both experiments, physiological tests will determine both metabolic and body temperature responses at thermoneutral and cold ambient temperatures. Some animals will also be placed in a thermal gradient to determine if normal preferred body and ambient temperature have been altered. Using an avian model of thermoregulatory development, the direct impact of microwave exposure on an immature animal will be assessed and predictions of the interaction between this potential stressor and other environmental agents will be improved.